Linkbolt - Seamless Link Sharing Connecting Devices, Unify Your Links.
Mailspring - Mailspring is a mail client for Mac, Windows and Linux.
Bigbee - Connect with anyone, anywhere.
Geary - Geary is an email application built for GNOME 3.
HealthyTogether.co - Hang out with friends in real life
The Bat - The Bat! is a secure desktop email client for Windows, designed to protect your correspondence against third-parties and to save your time.